Electronic amplifier



w. G. H. FINCH 2,075,604

ELECTRON I G AMPLIFIER March 30, 1937.

Filed Nov. 11, 1935 2 U INPUT 22 OUTPUT V15 as ef 1NVE NTOR. wilhamjJCJZnch BY 2 Q E Z ATTORNEY.

' Patented Mar. 30, 1931 UNITED STATES P TENT OFFICE This invention relates to electronic amplifiers, and more particularly relates to novel circuits for selectively amplifying electrical signals. I The circuits for amplifying electrical signals 5 in ordinary use are essentially amplifier tubes v cascaded by means of transformers, resistancecapacity coupling or inductance-capacity. coupling. These systems inherently cause distor-- tion due to reduced amplification of'- the lower i audio frequencies as is well known, and moreover, do not amplify direct current signals- Direct current amplifiers generally are electronic circuits wherein amplifier stages are cascaded with direct connection between the plate of one tube and the grid of the next succeeding tube. However, the succeeding tubes in the direct current amplifiers heretofore generally used have the undesirable feature of requiring an independent ungrounde'd plate battery supply for each-stage or a potential supply equal to the sum of the plate potentials necessary for each stage.

The operation of my present invention depends upon a novel amplifying circuit which maybe.

used to amplify uni-directional currents of zero frequency up to signals of extremely high frequency with no discrimination in any frequency band. I also provide means wherein my circuit may be modified to amplify any desired frequency band and reject the other frequencies in- 0 troduced to the input of the amplifier. The amplifierzcircuit, according to my invention, em-

ploys a common battery supply for all stages which are cascaded.

Accordingly, an object of my invention is to 35 providenovelelectrical. signal amplifying circuits.

Another object of my invention is to provide a novel electronic circuit for selectively amplifying electrical signals ranging from zero frequency (uni-directional) to extremely high frequencies 40 with substantially no phase shift or frequency discrimination. Still another object of my invention isto provide a novel electronic amplifier circuit for selective telegraphic signal operation using a com- 5 mon grounded potential supply for all cascaded stages. v

A further object of my invention is to provide a novel direct coupled electronic circuit for amplifying signals of predetermined frequency bands 50 to the exclusion of all other signals.

Still a'further object of my 1- vention is to provide a novel amplifier circuit for operating a telegraph repeater'relay using the amplifier principles outlined in my present invention. 55 These and other objects of my inventionwill become apparent in the description to follow in connection with the drawing, in which:

Figure 1 is a circuit diagram of three stages of an amplifier. using the principle of my invention. Figure 2 is a circuit diagram of the amplifier of my invention employing two predetermined frequency bands to selectively actuate a receiver relay.

The electrical signal to be amplified is introduced to the input terminals 8 and 9 of the am- 10 plifier shown in Figure 1. The terminals 8 and 9 conducts the signals to the grid Ill and cathode II respectively of the thermionic .vacuum tube V--'l. The cathode or heater ii is preferably connected to ground potential. The input grid circuit biasing battery A maintains the grid It at its normal operating negative potential with respect to the cathode II and is connected thereto through the grid resistor R-l. The positive terminal l3 'of the anode circuit potential supply B is connected to the anode l2 through the anode resistor R-2. A resistor R 3 is connected between the anode I! of vacuum tube V--i at point I and the grid iii of vacuum tube V-2 at point IS. The negative terminal I! of battery C is connected to a resistor R-4 which is in turn connected to the grid It at point 15 as shown in Figure 1. The positive terminal of potential supply C is connected to ground.

With no signal input to vacuum tube V-l normal anode current will flow through resistor 3-2 and cause a potential drop across resistor R-2, so that point I will have a lower voltage value than point IS. A circulating current will flow in the local circuit comprising battery B, resistor R2, resistor R-3, resistor 3-4, and battery C. 'The function of battery C is to make the potential of point ISsufiiciently negative to be equal to the normal or'predetermined biasing. potential for the grid ii of the vacuum tube V-2 with respect 40 to its cathode. 18. Accordingly, the value of the voltage of battery C is of the orderof the voltage of the B battery in this circuit according to my invention. The relative values of the resistors R-2, R--3, and R-l depend upon the particular type of tube used and upon the voltages of the B and C batteries, and also depend on the other'circuit parameters. I thus provide proper operating potentials for the anode of the tube V-i' and the grid of the tube V-2 by the resistor coupling circuit herein disclosed. A current flows through the resistance R-3 to cause a potential drop to reduce the normal positive plate voltage at point hi to the proper negative biasing voltage for the succeeding grid "5 at point I5.

When a positive signal or impulse is'applied to the grid ill of the tube V-.-l, the space current in tube V-| increases, as will the current flowing through the anode resistor R-2. The potential of point I will accordingly be lowered because of a correspondingly increased potential drop across resistor R-2. Accordingly. thepotential drop across resistors M and R4 in series will become less because the potential source of battery C is at substantially constant potential and the potential of point ll has decreased. The potential of point IE will therefore be correspondingly lowered. A positive signal impulse introduced to the grid i0 of tube V-i, is accordingly repeated as an amplified but negative signal to the grid it of the next tube V2. A phase reversal of 180 is produced upon the signal between these points.

I have illustrated in Figure 1, a further stage of amplification which is identical with that herein described. Resistor- M is the load resistance of tube V2 and is connected between point i9 which connects to the positive terminal of the B battery and the point 20 connecting to the anode 2|. A resistor R 6' is connected between point 20 and point 2|. Resistor R-l is connected between points 2i and the negative side i! of-battery C. Resistor R-5 corresponds to 3-2, R-G to R3, and R-l to R4. A circulating current fiowsthrough the local circuit comprising the battery B, resistors R5, R-6; and R! and battery C. The resistors R-i, R-6, and Rl are so proportioned that the proper anode potential is applied to anode 20' of the tube V--2 and the proper negative or predetermined biasing potential is applied to the grid 22 of the vacuum tube V-3 with respect to the cathode 23.

The amplified negative signal or impulse at grid i6 causes a decrease in the normal anode current which fiows through resistor R-S there-.

and introduced to tube V-2, 180 out of phase,

with respect to the phase of the signal input, as will now be evident. Tube V-2 in turn further amplifies the amplified reversed phase signal and introduces it to the grid 22 of the third vacuum tube V--3, reversed 180 again. The original weak signal at the input terminals 8 and 9 0f the amplifier of Figure 1 accordingly appears in substantially its original wave form and original phase relation but with greatly amplified magnitude at the input point 2| of the thermionic vacuum tube V3. Further stages of amplification beyond tube V-3 are feasible in a similar manner. I have shown the anode 24 and the positive B battery terminal l3 connected to the output terminals 8' and 9' respectively. The ampliiied signals, however, may be connected to any suitable translating device or be transmitted by line wire'or radio to a distant point, or be further amplified as desired.

The amplifier hereinabove described in connection with Figure 1 amplifies uni-directional signals (zero frequency) as well as extremely high frequencies with no frequency discrimination if proper design precautions are taken. 7 This amplifier may for example be used in television re ceivers. Television signals ordinarily comprise a band width from 10 cycles or less to about 200,000

cycles. The amplifier of Figure 1 may readily be designed to amplify a range of frequencies from zero up to 200,000 cycles with negligible distortion .and phase shift. The resistors used in such a The outstanding advantages of thedescribed direct current 'amplifler are that the succeeding cascaded stages are all connected to a common relatively low voltage battery supply, one end of which is at ground potential, and that the cathodes of all the amplifying tubes are at substantially the same potential. I have shown all cathodes as preferably connected to ground potential. The filament or heater supply for the vacuum tubes may accordingly be of any preferred type.

The selective telegraphic signal amplifier circuit of my present invention is illustrated in Figure 2. The electrical signals to be amplified are introduced at the input terminals and of the circuit of Figure 2. The input terminals are connected between ground and the point 25'. The input circuits of the vacuum tubes V-l and V-G are connected in parallel so that grids 26 and 21 of vacuum tubes Vl and V-G respectively are both connected to the point 25. The negative terminal of the biasing battery A is connected to grid resistor R-l' the other end of which is connected to the point 25. The grids 26 and 21 are properly biased with respect to their cathodes 28 and 29.

An inductance L-8 in series with a resistance R-B is connected to the anode 30 of tube V-4 to form the load impedance thereof. The positive terminal 3| of the B battery provides the anode potential supply. Point 32 is at the anode 30 potential and is lower in value than the voltage at terminal 3| by the normal direct current potential drop across R-8 and L8 with no signal input. Inductance L-9 and resistor R- -S are connected in series between points 32 and 32 corresponding to a metallic or conductive coupling between the anode 30 of tube V4 and grid 34 of tube V-5. Inductance L-i0 and resistor R-.-i0

and battery C. Resistor R-8 and the potential of the B battery are proportioned to produce a normal operating anode 30 potential for tube V4 at point 32. The voltage of the C battery is of the same order of magnitude as that of the B battery and serves to make the potential ofthe grid 34 at point 33 of proper negative biasing value. A direct current potential drop occurs between-points 32 and 33 equal to the diiference between the normal operating potential of anode 30, and the normal biasing potential of grid 34 at zero signal impulse. The inductances permit the use of smaller voltage sources for producing required electrode operating voltages as is well known in the art.

The inductors may be air-cored, ironcored or have metal cores of high permeability. The inductances of the coupling circuit herein described between tubes V-l and V5 may be considered as components of three arms of a pi-type filter and suitable condensers may be connected across them to form a band pass filter for a predetermined frequency band. I have illustrated condenser 0-8 connected in parallel with inductance L-8. This parallel circuit may be made to be resonant at, for example, 800 cycles. The impedances between points 32 and 3| will be relatively very high at the resonant frequency of 800 cycles and correspondingly much lower for frequencies of resonance as is well known in the communications art. The amplificaton of the input signal by tube V-l will correspondingly be a maximum for only the predetermined frequency, and will tend to suppress all other frequencies, particularly those remote from the resonant frequency. The predetermined fre-- quency signal which corresponds to the -resonant frequency of the parallel resonant circuit L-8, 0-8 is introduced to the succeeding,

vacuum tube V--5 through the arm L-S and R-9 of the coupling circuit. ,The predeterminedfrequency signal is further amplified. by vacuum tube V--5, the output of which is connected to the alternating current relay 31 01 the repeater relay 38."

Another selective amplifier circuit is con-- to the common input terminals of the circuit at point 25. The anode arm includes inductance L-|I and resistance R-l|, the coupling arm, inductance L-l2 and resistance R--l2; and the grid arm, inductance L--l3 and resistance R--'l3 The common 13 and 0 battery are used. A condenser C-ll is connected across the inductance L-ll and tuned to the second predetermined frequency, for example, 1200 cycles. The 1200 cycle component of the input signal is accordingly selected by the amplifier section compris ing tubes V-6 and V-l, and is amplified and introduced to the alternating current relay 39 of the repeater relay 38.

The circuit of Figure 2 is used to segregate and amplify two predetermined frequency signals and introduce them to the corresponding coacting alternating current relays 31 and 39 of repeater c0 relay 38. The 800 cycle signal may be made to correspond to a spacing impulse, and the 1200 cycle signal to a marking impulse for suitable local translating apparatus such as for printing telegraphy and the like. cycle-signal impulses may be transmitted over ,a land line to the input terminals of the circuit of Figure 2; or may be made to modulate a radio frequency carrier wave for radio transmission to the distant receiver which detects the original modulating signals and introduces them to the input of my selective amplifying circuit. Telegraphic communication using two-ton' electrical signals for positive actuation at the translating 75 apparatus with corresponding marking and spac- The 800 and 1200 ing impulses'may readily be carried out with the circuit of my present invention. A marking impulse may be used to correspond to the 800 cycle frequency; the spacing impulse, to the 1200 c I cycle frequency. when a marking impulse of 800 cycles occurs, it is selectively amplified by section 37-4, V-B and introduced to the relay 31-which attracts the pivoted armature to energize a local marking M circuit as is well known in the communications art. When a spacing impulse corresponding to a 1200 cycle signal occurs, it is selectively amplified by section V-G, V| and introduced to the relay 39 which attracts the pivoted arm 10 to actuate the spacing 8 contacts of the local circuit. Terminals 4| connect the translating relay 38 to the local circuit.

Although I have described a preferred embodiment of my present invention, modifications may be made which fall within the broader spirit and scope thereof and accordingly I do not intend to be limited, for -example, by any particular type of vacuum tube employed, by the type of coupling impedances used, by the frequency ranges or hands for the amplifiers or to their applications except as set forth in the following claims.

I claim:

1. In a signalling system, a pair of thermionic tubes, each having an input circuit connected in parallel; anode electrodes for each of said tubes; a second pair of thermionic tubes having cathode, anode and control electrodes; metallic connections from each of the anode electrodes of the first pair of thermionic tubes to the con-' nections from each of the anode electrodes of the first pair of thermionic tubes to the control electrodes of their associated thermionic tube of said second pair; impedance means including .circuit connectionsto said metallic connections for by-passing all frequencies except predetermined bands individual to each of said metallic paths and a common source of anode potential for all of said thermionic tubes.

3. In a signalling system, a pair of thermionic tubes, each havingan input circuit connected in parallel; anode electrodes for each of said tubes; a second pair of thermionic tubes having cathode, anode and control electrodes; me-

tallic connections from each of the anode electrodes of the'first pair of thermionic tubes to the control electrode of the associated thermionic tube of said second pair; impedance means including circuit connections to said metallic connections for by-passing all frequencies except predetermined bands individual to each of said metallic paths and a common source of anode potential for all of said thermionic tubes.

4. In a signalling circuit, a cathode and an anode forming an electronic stream path therebetween; a second set of electrodes comprising a cathode, anode and a control electrode formring a second electronic stream path; a metallic connection including a first resistance and first path to said control electrode; a common anode potential source for said paths; a second common potential source; impedance means including a second resistance and second reactance connecting said first mentioned anode. to said common anode potential source; further impedance means including a third resistance and third reactance connecting said control electrode and said second potential source; said first, 10 second and a third resistances and potential sources forming a series circuit for producing a potential drop in said first resistance to obtain a predetermined bias on said control electrode; said-first, second and third reactances forming 15 a selected frequency network for by-passing all frequencies except a predetermined band from said first mentioned anode and said control electrode.

5. In a signalling circuit, a cathode and .an 23 anode forming an electronic stream path therebetween; a second set-of electrodes comprising a cathode, anode and a control electrode forming a second electronic stream path; a metallic connection including a first resistance and first Z5 reactance from the anode of said first stream path to said control electrode; a common anode potential source for said paths; a second common potential source connected to said first source; impedance means including a second re- 33 sistance and second reactance connecting said first mentioned anode to said common anode potential source; further impedance means includ ing a third resistance and third reactance'connecting said control electrode and said second potential source; said first, second and third resistances and potential sources forming a series circuit for producing a potential drop, in said first resistance to obtain a predetermined bias on said control electrode; said cathode electrodes -be'ing maintained at substantially the same potential, and the interconnection of said sources being also connected to said cathodes; said first, second and third resistances forming a selective frequencynetwork for by-passing all frequencies except a predetermined band from said first mentioned anode and said control electrode.

6. In an amplifying circuit, a plurality of pairs of amplifying electron stream paths, each path including a cathode, anode and control electrode;

'the interconnection between said sources; circuit connections including a second resistance and second reactance extending from a plurality of said anodes to a terminal of said anode source; further circuit connections including a third resistance and third reactance extending from the control electrodes of a plurality of said paths to a terminal of said second source, all of said circuit connections controlling the application of the anode potential to their respective anodes and maintaining a predetermined bias potential on their respective control electrodes; said first, second and third reactances forming a selective frequency network for by-passing all frequencies except a predetermined band from the anode of each of said electron paths to the control electrode of the next succeeding path.

WILLIAM G. H. FINCH. 

